Lissafta fadin rufin a m² bisa girman ginin, nau'in rufi da kusurwar gangara — tare da faɗin baki da ajiya don kayan rufi.
| Nau'in rufi | Dabara |
|---|---|
| Rumbu | rafter = width/cos(angle); area = rafter × length |
| Gable | rafter = (width/2)/cos(angle); area = 2 × rafter × length |
| Hip | rafter = (width/2)/cos(angle); ridge = length − width; area = rafter × (2×ridge + width) |
| Lebe | yanki = faɗi × tsawo |
Girman (faɗi/tsawo) ana ƙara su a lissafin ta hanyar ɓangaren rufin da ya wuce a ɓangarorin biyu. Ana amfani da dabarar hip lokacin da duk gangaren huɗu suke da tsayi ɗaya kuma tsawon ginin > faɗinsa.
Ga gidajen zama, matsakaicin gangare shine 30–45°. Ana amfani da gangare mai zurfi (15–25°) ga gine-ginen amfani, mafi tsayi (sama da 45°) — ga rufin soro/loft.
Tsawon katako yana ƙaruwa yayin da kusurwa ke ƙaruwa (rabawa da cos), don haka yankin rufin yana girma da sauri fiye da yankin bene na ginin.
10–15% daidai ne — yana rufe mahaɗar tudu, kwari da kwatangwalo. Ga rufin da suka haɗa (masu yawa, tagogi) — har zuwa 20%.
e-Buhalteris na taimaka maka wajen bin diddigin kayan aiki, ajiya da kuɗaɗen aiki.
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